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If you can tolerate a couple of seconds delay after pairing, a monostable would do the trick. Wire it so that when it's active it's providing the "off" output. Set it's interval to a bit longer than a whole on/off cycle when the b/t is un-paired. Then when it's paired the mono stops being triggered and the output stays high. A 74HC123 will do the job nicely. A 555 will do it if you can tolerate the output being the wrong polarity (so you would need to invert it).
Some people would be reaching for a microcontroller at this point - there are some 8 pin ones and you'd need no other parts so it's a tidy solution. Also there is the advantage you could program it to read the actual "connected" message from the b/t. Of course you do have to actually program it which might be getting too involved.
Thank you for that information throbscottle. I am trying to do this without a lot of programming. But I do know that I am going to have to program each unit with a different password.
I'm pretty sure there is a processor onboard. And I know that you can program it to do certain things. All I want it to do is to change the state from low to high when it comes into range with a "paired" phone.
As far as I am aware, those BTv5 modules do not "pair"?
When I've used them, an ad-hoc connection is set up for the duration of a data transfer, then taken down again when no longer needed.
One end of the required link needs to request a connection each time a new data transfer session is required.
Or for just "presence detect" you could probably tell the module to search available connections then match the ID of the device(s) you want to trigger the relay.
That would need an MCU of some sort to interact with the BT module, issue commands and parse the responses.
I have a similar setup on my home automation system, a plugin that uses a USB bluetooth dongle to detect certain phones and recognise that the owner is in the house.
I know that there has to be a way to do this. Other Bluetooth devices don't need an app on the phone to be able to "connect". Why should an hc05 be any different? I just need it to connect so that the state will change from low to high.
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